Display devices, such as Liquid Crystal Display (LCD) devices and Plasma Display Panel (PDP) devices, may include a display driver IC (DDI) therein. A display device may include a plurality of source driver chips (i.e., source drivers) having a DDI configuration. Each source driver may include driver source lines (e.g., data lines) of a panel based on display data of a timing controller. As a backward signal line, a shared back channel (SBC) may be used as a dedicated bus for transferring a soft fail signal output from any of the source drivers to a timing controller. Herein, the soft fail signal may indicate an unlocking state of a clock recovery unit or whether setting values are changed due to Electro-Static Discharge (ESD). When a clock is locked, the soft fail signal may be set to a logical high level by a turn-off operation of a shared back channel driver within a source driver. When a clock is un-locked, the soft fail signal may be set to a logical low level by a turn-on operation of the shared back channel driver within the source driver. Examples of display driver ICs are disclosed in U.S. Pat. No. 7,259,742 to Chang et al. and U.S. Pat. No. 7,737,939 to Shin et al., the disclosures of which are hereby incorporated herein by reference.